President Obama is reviewing a final list of military options as his Pentagon chief said US forces are set to punish the brutal Syrian regime for last week’s horrific poison-gas attack.

“We are ready to go,” Defense Secretary Chuck Hagel said.

Four US destroyers are positioned in the eastern Mediterranean Sea to hit key Syrian military bases, launch sites, air defenses and command centers with dozens of Tomahawk cruise missiles, officials said.

Other options on Obama’s desk include long-range bombing raids, missile launches from submarines and strikes at targets close to President Bashar al-Assad’s heart, such as his presidential palace in Damascus.

The attack by NATO allies, with growing international support, is expected to begin by the weekend and last two or three days.

The war jitters sent stock markets plunging, drove the price of oil to a two-year high and fueled fears of Syrian retaliation against US allies Israel and Jordan,

Obama spokesman Jay Carney all but confirmed an imminent US attack — while insisting its intent was not to drive Assad from power. ”The options we are considering are not about regime change,” he told reporters in Washington.

He said a US intelligence report would, likely to be released this week, will remove any doubts about the Assad regime’s guilt in the predawn poison-gas attack last week that killed an estimated 1,300 Syrians, many of them children, as they slept.

As the world braced for Obama’s biggest military action as president, there were several developments:

* Assad warned that the United States would face “what it has been confronted with in every war since Vietnam: failure.”

His foreign minister, Walid al-Moallem, said his country would use “all means available” to defend itself. “We have the means to defend ourselves and we will surprise everyone,” he said.

* Iran said an attack on its ally Syria would threaten “the region’s security and stability” — a veiled hint that pro-Iranian Hezbollah might strike Israel from its bases in Lebanon.

* Israeli Prime Minister Benjamin Netanyahu said his country “will react, and react fiercely” if attacked. Israel officials reported a surge in requests by civilians to replace old gas masks.

* Russia, a longtime sponsor of Assad, denounced the war preparations. The West is acting “like a monkey with a hand grenade,” Deputy Prime Minister Dmitry Rogozin said.

* But American allies, including France, Canada, Turkey, Italy, Australia and Britain, rallied behind the US hard line.“France is ready to punish those who took the heinous decision to gas innocents,” French President François Hollande said.

Officials said a military strike is unlikely to begin while UN arms inspectors are still in Syria or before British Prime Minister David Cameron convenes an emergency meeting of Parliament tomorrow to vote on a motion clearing the way for the Britain’s participation in a NATO strike against Assad.

Officials said the targets will not include chemical-weapons arsenals because airstrikes could release poison gas or allow radical groups to gain control of chemical-weapon stockpiles.

Instead, war planners may take aim at prime targets near Damascus, such as the military base of Syria’s 4th Armored Division, led by Assad’s younger brother, Maher.